The present invention relates to a countershaft transmission in which a plurality of speed change gear trains are disposed in parallel with one another on parallel shafts, and a gear change is carried out by selectively activating one of the clutches provided to the gear trains.
1. Field of the Invention
Many countershaft type transmissions are used in automobiles, and an example of a countershaft transmission is disclosed in Japanese Laid-open Patent Publication No. H6(1994)-221432(A). Typically, a countershaft transmission comprises a plurality of constant mesh type speed change gear trains, which are disposed in parallel with one another between two parallel shafts, and each gear train is provided with a clutch, for example, a synchromesh-type clutch. These clutches are activated selectively in correspondence to the manipulation of the shift lever by the driver to achieve a power transmission at a desired speed ratio.
2. Description of the Related Art
There is an attempt to increase the number of speed change ratios or gear ratios available for such countershaft transmissions, in order to improve the driving characteristics of the vehicles which incorporate countershaft transmissions. With this attempt, the number of speed change gear trains which are disposed in parallel with one another between the two parallel shafts is also increasing. This trend may lead to a problem that the size of the transmission will increase to include the shafts which are formed longer than ever to support these gear trains, which are increasing in number. Therefore, not to elongate the shafts too much for the purpose of keeping the transmission compact, there is a demand for improvements in the arrangement and construction of the speed change gear trains.
In the production of a countershaft transmission, the relation of the two parallel shafts must be maintained while a plurality of speed change gear trains each including drive and driven gears to mesh with each other are being mounted on these shafts, together with a plurality of clutches which select the gear trains for power transmission. Therefore, there is a need for a countershaft transmission which facilitates easy and simple assembly.